A well-known drive-by-wire-type accelerator pedal device, which is a pedal-operated operation device, for use in a vehicle, such as an automobile, has a pedal, which serves as an operating element to be foot-operated; a housing, which serves as support means for supporting the pedal in a pivotally movable manner; a return-urging spring for urging the pedal relative to the housing in a direction opposite the direction in which the magnitude of operation of the pedal is increased; a sensor for detecting the amount of pivotal displacement of the pedal relative to the housing; and a slide portion for imposing a hysteresis load on a pivotal movement of the pedal by means of a friction force. Such an accelerator pedal device is described in, for example, Japanese Patent Application Laid-Open (kokai) No. 2005-14896.
According to an accelerator pedal device of this kind, the slide portion generates a friction force, and a hysteresis load induced by the friction force reliably imparts hysteresis to the relation between a tread force imposed on the pedal and the amount of pivotal displacement of the pedal. Thus, as compared with an accelerator pedal device whose hysteresis is low, a driver can more readily control a vehicular drive force through his/her treading on an accelerator pedal.
In an accelerator pedal device of the above-mentioned type, when a hysteresis load is set high so that a driver can readily maintain the magnitude of treading on an accelerator pedal at a constant value, a tread force required for starting a pivotal movement of the accelerator pedal becomes excessively high; thus, the driver feels a so-called feeling of treading on a wall when he/she starts treading on the accelerator pedal. Also, since the accelerator pedal does not return unless the tread force is reduced greatly, when the driver eases off the accelerator pedal, he/she feels a feeling of defective return of the accelerator pedal.
By contrast, when the hysteresis load is set low, there can be mitigated a feeling of treading on a wall at the time of start of treading on the accelerator pedal and a feeling of defective return of the accelerator pedal at the time of easing off the accelerator pedal. However, in this case, for example, even when the tread force varies slightly in association with vibration or the like of a vehicle, the stroke of treading on the accelerator pedal varies; thus, the driver encounters difficulty in maintaining the magnitude of treading on the accelerator pedal at a constant value.